A 32-year-old woman presents with recurrent petechiae on her lower limbs over 2 years, accompanied by intermittent epistaxis and gingival bleeding. Physical exam: scattered petechiae and ecchymoses on lower limbs, no hepatosplenomegaly. Laboratory tests: Hb 110g/L, WBC 5.1×10<sup>9</sup>/L, PLT 35×10<sup>9</sup>/L. Bone marrow smear shows 296 megakaryocytes per slide, with 90% being granular type. The mechanism of thrombocytopenia is: